Lead-through insulator, particularly for high voltage mercury vapour tubes



1967 MAX-JOSEF SCHONHUBER LEAD-THROUGH INSULATOR.

3,3005 74 PARTICULARLY FOR HIGH VOLTAGE MERCURY VAPOUR TUBES 2 Sheets-Sheet 1 Filed Feb. 21, 1966 Ma.xJaseF Schb'h/wber United States Patent Oflfice 3,300,574 LEAD-THROUGH INSULATOR, PARTICULARLY FgR HIGH VOLTAGE MERCURY VAPOUR T BES Max-Josef Schiinhuber, Zurich, Switzerland, assignor to Aktiengesellschaft Brown, Boveri & Cie, Baden, Switzerland, a joint-stock company Filed Feb. 21, 1966, Ser. No. 528,704 Claims priority, application Switzerland, Mar. 3, 1965, 2,965/ 65 9 Claims. (Cl. 174-142) The invention relates to a lead-through insulator or bushing, in particular for high voltage mercury vapour tubes, having a supply line passing through the insulator and electrodes interposed between the conductor and the remaining parts for the potential control, said electrodes surrounding at least partly the current conducting parts.

Such insulators are used in particular with high voltage mercury vapour tubes, in high voltage direct current transmission, where they are used for the supply of current to the anode of the tube.

It is known to provide screens or electrodes in the interior of insulators in order to improve the potential distribution. It is an easy matter to provide these electrodes when solid insulators are used, consisting of hard-paper or casting resin, as they lie in a solid dielectric, and do not require special fixing. The electrodes must be staggered, with the electrode nearest to the conductor extending to the vicinity of the installation of the conductor, the next starting somewhat lower down, as there the potential is less, and the next electrode even lower, and so on. At the level of the flange by which the insulator is fixed to the housing of the mercury vapour tube, all electrodes must be present, so that the electrical field can build up evenly from the flange to the conductor, and at that place the closest positioning, and control of the potential, are particularly important.

When hollow insulators are used, the screens must be held in position. Fixing at the periphery of the insulator, for example on the porcelain, is difficult, as this if possible must be bored or divided by the interposition of metallic rings. An arrangement is known in which the potential-control electrodes are arranged as tubes around the conductor, which for example can be the anode supply line, with the individual electrodes fixed in such a way that they are carried at a fixed distance from each other with interposed insulators separating them, the entire arrangement of interposed electrodes of a mercury vapour tube, held together in this way, being mounted on the iron container. In an intermediate electrode system with external voltage control, connections have to be made through the insulator for applying voltages to one or more of the electrodes.

The disadvantage of this arrangement is that the interposed insulators lie in a region of high field density, and thereby, as a result of the voltage stress present over the whole length, the permissible surface field strength and limiting voltage of the whole lead-through insulator arrangement is restricted. There is furthermore the disadvantage with anode supply lines to mercury vapour tubes that because of the continuously coaxial arrangement of the electrodes, charged particles from the tube may enter the control chamber and reach the upper end. This, too, unfavourably influences the dielectric strength.

The invention consists in a lead-through insulator, having a conductor passing through the insulator and intermediate electrodes interposed .between the conductor and the remaining parts of the insulator for potential control, said electrodes at least partly surrounding the conductor and being sheets of which all are fixed along the insulator wall and at least some are bent back on themselves 3,3005 74 Patented Jan. 24, 1967 and then are bent again in their original direction in such a way that the distance between adjacent sheets is substantially constant except where the sheets are bent to pass along the insulator wall.

The electrode sheets which are illustrated need not be made from a single piece but rather can also consist of several sheet parts which are assembled and secured together by welding or soldering.

FIGURES 1 to 5 of the accompanying drawings illustrate in vertical section five exemplary embodiments of the invention.

FIGURE 1 shows in section part of a lead-through insulator traversed by a current conductor 1, for example, the anode supply line of a mercury vapour tube installed in the insulator only the right-hand wall of which is shown. Two intermediate electrodes 3 and 4 can be seen in FIGURE 1 lying between the said anode supply line 1 and the other parts of the arrangement, for example, the control grids, the flanges of the insulator and so on, which are not shown in detail. Electrode 3 is closely connected to the supply line 1, and accordingly has its potential; the second electrode 4, is arranged at a fixed distance from it, and electrodes 3 and 4 have shapes such that the electrical field is as even as possible, and occurs only between them. The electrode 3 extends away from conductor 1 initially into a semi-circular shape, then extends downwardly parallel to the supply line 1, and bends upward again; the bending radius must be large enough to prevent crowding of the field lines, and should amount to at least 1 cm. The electrode sheet then passes upwardly next to the insulator wall 2. The distance from the insulator wall must be the least that will avoid point contact with the insulator wall, which is not completely smooth. The said distance should be at least 1 mm. The intermediate electrode is now fixed to the wall by a spring ring 6 clamped to the wall. The electrode sheet can be screwed to this spring ring, or fixed in some other way. It can be seen that the fixing screws lie in a space within a re-entrant part of the sheet where there is zero field strength, and accordingly the shape of the fixing is unimportant for the field strength distribution.

The electrode 4 is now exactly adapted to the shaping of the electrode 3. Initially it runs exactly parallel thereto, until the lower bend of electrode 3, where electrode 4 bends downwardly and can if desired be fixed to the wall 2. Thus the sheets are parallel and at a constant distance from each other until the insulator wall is reached, this has the advantage that the resistance to flashover is the same at all places. The distance is a function of the known breakdown conditions at low pressures, and is the same even at the bends in the interior of the insulator, being somewhat greater only where the intermediate electrodes bend away along the insulator wall, for example between the points 4 and 14. This, however, is advantageous, since at this place a greater distance leads to a greater dielectric strength. This can take place in the same way as with the first intermediate electrode. If the insulator consists of a plurality of parts, assembled on metal flanges 7, as is shown in FIGURE 1, then the sheet can be screwed on directly only if a distance-piece 8 is used. In this case an electrical field forms only between the various electrodes. Within the individual bend of any one electrode the field strength is zero. The only advantage the bends now have is that they can catch charge carriers, so that these cannot reach the end of the bushing. With multiple staggering, as shown, for example, in FIG- URE 4, the path upwards for charge carriers is blocked.

In FIGURE 2 another embodiment is shown. The first electrode sheet 3, lying directly on the anode supply line 1, initially expands away and then passes immediately upwardly, with the result that an anode-enlarging is obtained. The electrode is fixed in the same way as shown in FIGURE 1. initially parallel to the electrode 3. The distance between the two electrodes is then gradually increased, with the result that the field lines spread in the direction towards the insulator wall 2. The sheet 4 then passes downwardly, along the insulator wall, where it is fixed, and then bends upwards again, keeping to the desired smallest radius of bending of 1 cm. until at 8 it again reaches a point where it contacts itself. There it is joined to itself, for example, by brazing or welding. There occurs in this way a hollow space 9-0f zero field strength. The spring ring 6 used for fixing lies in a groove of the insulator, so that it cannot slip out. Furthermore, in this embodiment, a third intermediate electrode is shown, which also runs parallel to the electrode 4 initially, and is then bent downwardly for fixing to the wall. With this arrangement, of course, further electrode sheets are possible in addition, in order to obtain still further subdivision of the potential control.

In FIGURE 3 a further embodiment is shown, in which the interposed electrode 3 initially bends away from the supply line, then passes upwardly again in the original direction, and then bent again to the wall 2. The remaining sheets 4 and 5 are adapted to correspond to this shape, and in this way an even larger space 9 of zero field strength occurs.

FIGURE 4 shows a whole insulator in-an arrangement similar to that of FIGURE 2 with four intermediate electrodes, and here the mounting on the mercury vapour tube is also shown. Here again, the reference number 1 designates the anode supply line and 2 the wall of the insulator, which is mounted on a tank 11 which represents the mercury vapour tube. The four control electrodes have the reference numbers 3, 4, 5 and 13, and are connected underneath the anode to the potential control grids 12, which are arranged in the space between the anode and the cathode in addition to the control grid. The arrangement shows that the field distribution is extraordinarily even, and that strong field concentrations are completely obviated. Furthermore, charge carriers can scarcely penetrate into the interior of the insulator.

FIGURE 5 shows a further embodiment of the invention, in which the loops formed by the electrode sheets extend upwardly. Here, too, the distance between the individual sheets remains constant. 7

With these arrangements, a lead-through insulator or bushing is obtained that has adequate dielectric strength right up to the highest voltages.

What I claim is:

1. A lead-through insulator having a conductor passing through the insulator and intermediate electrodes interposed between the conductor and the remaining parts of The second electrode 4. is, here again,

' 4 the insulator for potential control, said electrodes at least partly surrounding the conductor and being sheets of which all are fixed along the insulator wall and at least some are bent back on themselves and then are bent again in their original direction in such a way that the distance between adjacent sheets is substantially constant except Where the sheets are bent to pass along the insulator Wall.

2. An insulator as claimed in claim 1, in which the sheet lying nearest to the conductor is bent back on itself towards the insulator wall and extends along the wall towards the conductor entry and is there fixed; each subsequent sheet is parallel to the previous sheet as far as the insulator wall, then bends back in the opposite direction of the insulator wall and extends along it, being fixed to the wall, then again bends inwardly in the first direction parallel to the Wall, until it abuts on itself, Where it is tangentially connected to itself, so that a pOtentiaLfree, closed hollow space results; and the final sheet is parallel to the previous ones as far as the wall, and then is bent towards the flange side of the insulator, and fixed there.

3. An insulator as claimed in claim 1, in which the sheet lying nearest to the conductor is bent from the conductor direction towards the insulator wall, then runs parallel to the wall, then is once again bent towards the insulator wall, and finally it extends along and close to the insulator wall.

4. An insulator as claimed in claim 1, in which, for fixing the sheets at the places where they lie close to the insulator wall, a groove is provided, in which is set a resilient ring, onto which the sheets are screwed.

5. An insulator as claimed in claim 1, consisting of a plurality of insulator members joined by metal parts, and in which the sheets are fixed to the metal parts at the level of the said parts.

6. An insulator as claimed in claim 1, in which the radii of curvature at which the sheets are bent are not less than 1 cm.

7. An insulator as claimed in claim 1, in which the sheet parts that extend along the insulator wall have a distance from the latter of at least 0.1 cm. and the resulting gap length between sheet and insulator wall amounts to at least fourfold the gap width.

8. An insulator as claimed in claim 7, in which each sheet is composed of a plurality of part-sheets that are fixed to each other.

9. An insulator as claimed in claim 1 for anode supply lines to mercury vapour tubes, in which the first intermediate electrode is connected directly to the supply line, and by the electrode the supply line is broadened at its upper end.

No references cited.

LARAMIE E. ASKIN, Primary Examiner, 

1. A LEAD-THROUGH INSULATOR HAVING A CONDUCTOR PASSING THROUGH THE INSULATOR AND INTERMEDIATE ELECTRODES INTERPOSED BETWEEN THE CONDUCTOR AND THE REMAINING PARTS OF THE INSULATOR FOR POTENTIAL CONTROL, SAID ELECTRODES AT LEAST PARTLY SURROUNDING THE CONDUCTOR AND BEING SHEETS OF WHICH ALL ARE FIXED ALONG THE INSULATOR WALL AND AT LEAST SOME ARE BENT BACK ON THEMSELVES AND THEN ARE BENT AGAIN IN THEIR ORIGINAL DIRECTION IN SUCH A WAY THAT THE DISTANCE BETWEEN ADJACENT SHEETS IS SUBSTANTIALLY CONSTANT EXCEPT WHERE THE SHEETS ARE BENT TO PASS ALONG THE INSULATOR WALL. 